The present invention relates to aqueous agents for treating wood and wooden materials.
Wood and wooden materials are widely popular construction materials. Due to their chemical composition and their structure, however, they possess certain naturally inherent disadvantages. For example, they are constantly exposed to the danger of attack by fungi, bacteria and insects. Additionally, large variations in their moisture content can occur having a negative effect on dimensional stability and, in the worst case, leading to fissures. Finally, their high flammability causes considerable problems from the safety technology point of view.
To more or less eliminate the above-mentioned disadvantages, it has been customary for quite some time to treat wood and wooden materials with a great variety of agents by any of a large number of methods before or after the wood has been worked on machines. Nowadays, it is even necessary in many fields of use for such treatments to meet regulating standards. In this connection, it is desirable to satisfy such requirements by simple, economical and environmentally harmless measures and to achieve an effect lasting for a maximally long period of time to avoid expensive aftertreatment processes. Particularly in the case of wood and wooden materials which are exposed to outside weathering and/or high moisture conditions, these objectives could not be completely realized heretofore.
The preferred, current methods for treating wood for preservation may be represented as follows:
(1) The introduction of wood preservatives, resistant to washing out and diffusion, from an aqueous solution. A good, durable impregnation of the marginal zones is normally achieved by this method, especially in a dipping process. However, the inner zones of thicker pieces of material are not successfully impregnated. Additionally, this method is incapable of preventing the occurrence of cracks caused by great moisture fluctuations; in part, unprotected zones are formed, since all active agents are fixed in the marginal zone. Attempts have been made to overcome this deficiency by simultaneously using, in certain cases, in addition to the fixable preservatives, water-soluble active agents which are not fixable and thus remain capable of diffusion. However, this protection is also not permanent when cracks occur, since the unfixed active agents are then washed out by the effects of the weather. If longer lasting protection is desired, an additional surface treatment by application of an organic coating is required. PA1 (2) The introduction of wood preservatives, which are water-insoluble or sparingly soluble in water, from organic solvents. The capability of these active agents to diffuse in wood having a sufficiently low moisture content is satisfactory; however, this method is likewise incapable of preventing cracks. Additionally, several of these often highly toxic preservatives have a marked vapor pressure. For these reasons, an additional treatment with an organic coating agent is also recommended here. Furthermore, a quite substantial disadvantage of this method is the use of organic, flammable and, in part, physically harmful solvents. PA1 (1) a double bond content corresponding to an iodine number of at least 200 g iodine/100 g, of which a double bond content of at least 100, also measured as the iodine number (g iodine/100 g) is due to cis-1,4-structural elements of the 1,3-butadiene polymer; PA1 (2) an amino group content of at least 50 mg-atoms of nitrogen/100 g of binder; and PA1 (3) a substrate polymer, for the amino-group-carrying 1,3-butadiene polymer having at least 70 molar percent butadiene units and a number average molecular weight of 500-6,000. PA1 (a) an adduct of 18-25% by weight of maleic anhydride and 82-75% by weight of a polybutadiene having a molecular weight (Mn) of 800-2,000, an iodine number of .gtoreq.350 (g iodine/100 g) and a cis-1,4-content of .gtoreq.70% of the double bonds present, with PA1 (b) a 1,3-diaminopropane of the formula ##STR1## wherein R.sub.1 and R.sub.2 independently are each alkyl of up to 4 carbon atoms or together represent --(CH.sub.2).sub.5 --or --(CH.sub.2).sub.2 --O--(CH.sub.2).sub.2 -, i.e., are components of a ring. PA1 (a) epoxidized polybutadiene with an epoxy content, determined according to DIN [German Industrial Standard]16 945, of 5-8% by weight of oxygen, prepared from a polybutadiene having a molecular weight (Mn) of 1,000-2,500, an iodine number of .gtoreq.350 g iodine/100 g, and a cis-1,4-content of .gtoreq.70% of the double bonds present, with PA1 (b) one or more amines of the formulae (2) ##STR2## wherein R.sub.4 and R.sub.5 independently are each alkyl of up to 4 carbon atoms or hydroxyalkyl of 2-4 carbon atoms, or in Formula (3) together represent --(CH.sub.2).sub.5 --or --(CH.sub.2).sub.2 --O--(CH.sub.2).sub.2 --, i.e., are components of a ring. Especially suitable is the use or concomitant use of 1,3-diaminopropanes of Formula (1). The amino group content in the final product is to be at least 120 mg-atoms of nitrogen/100 g of binder.
The above mentioned post treatment of the impregnated components with an organic coating normally takes place in a separate operating step. However, efforts have already been made to obviate this additional treatment step by the use of binder-containing wood preservatives. In these agents, synthetic resin dispersions were preferably used as the binders for the ingredients applied from aqueous solution, and alkyd resins and related systems were preferred for those applied from organic solvents.
One disadvantage in both cases is the low penetrating power of the organic binders. Additionally, for the binder-containing wood preservative systems, based on organic solvents, the binder content must be kept at a very low value; otherwise, the penetration of the preservative active agents is impeded. This makes it necessary to repeat the treatment until sufficient film thicknesses have been achieved. As a result, this mode of operation does not offer any economical advantages over a subsequent coating step. Moreover, the penetrating power of aqueous synthetic resin dispersions is even lower than that of the organic solvent-containing systems. Accordingly, the wood preservation effect attainable in all cases is moderate at best.
Consequently, the active ingredients added to aqueous impregnating agents serve more for preserving the coating agent prior to impregnation than for protecting the substrate to be treated. There is almost no regulation of moisture absorption and emission by the treated wood.
The known water-dilutable alkyd resin emulsions alkyd-resin-containing synthetic resin dispersions and water-dilutable alkyd resins are also subject to essentially the same disadvantageous features discussed for the water-dilutable glazings based on synthetic resin dispersions.
Prior to treating coniferous woods with the latter agents, priming with an officially admitted, wood-preserving primer is recommended or even required.